Opisthorchis viverrini
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''Opisthorchis viverrini'', common name Southeast Asian liver fluke, is a food-borne
trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...
parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...
from the family
Opisthorchiidae Opisthorchiidae is a family of digenean trematodes. Opisthorchiidae have cosmopolitan distribution. The most medically important species in the family Opisthorchiidae are '' Clonorchis sinensis'', ''Opisthorchis viverrini'', and ''Opisthorchis f ...
that infects the
bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. ...
. People are infected after eating raw or undercooked fish. Infection with the parasite is called opisthorchiasis. ''O. viverrini'' infection also increases the risk of
cholangiocarcinoma Cholangiocarcinoma, also known as bile duct cancer, is a type of cancer that forms in the bile ducts. Symptoms of cholangiocarcinoma may include abdominal pain, yellowish skin, weight loss, generalized itching, and fever. Light colored stool ...
, a cancer of the
bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. ...
s. A small, leaf-like fluke, ''O. viverrini'' completes its lifecycle in three different animals. Snails of the species ''
Bithynia Bithynia (; Koine Greek: , ''Bithynía'') was an ancient region, kingdom and Roman province in the northwest of Asia Minor (present-day Turkey), adjoining the Sea of Marmara, the Bosporus, and the Black Sea. It bordered Mysia to the southwest, Pa ...
'' are the first intermediate hosts, fish belonging to the family
Cyprinidae Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...
are the second intermediate host, and the definitive hosts are humans and other mammals such as dogs, cats, rats, and pigs. It was first discovered in the Indian
fishing cat The fishing cat (''Prionailurus viverrinus'') is a medium-sized wild cat of South and Southeast Asia. Since 2016, it is listed as Vulnerable on the IUCN Red List. Fishing cat populations are threatened by destruction of wetlands and have declin ...
(''Prionailurus viverrus'') by M.J. Poirier in 1886. The first human case was discovered by
Robert Thomson Leiper Robert Thomson Leiper (17 April 1881 – 21 May 1969) FRS CMG was a British parasitologist and helminthologist. Early life and education Leiper was born on 17 April 1881 in Witch Road, Kilmarnock, Scotland; the eldest of three children of John ...
in 1915. ''O. viverrini'' (together with ''
Clonorchis sinensis ''Clonorchis sinensis'', the Chinese liver fluke, is a liver fluke belonging to the class Trematoda, phylum Platyhelminthes. It infects fish-eating mammals, including humans. In humans, it infects the common bile duct and gall bladder, feeding o ...
'' and ''
Opisthorchis felineus ''Opisthorchis felineus'', or cat liver fluke is a trematode parasite that infects the liver in mammals. It was first discovered in 1884 in a cat's liver by Sebastiano Rivolta of Italy. In 1891, Russian parasitologist, Konstantin Nikolaevich V ...
'') is one of the three most medically important species in the family Opisthorchiidae. In fact ''O. viverrini'' and ''C. sinensis'' are capable of causing cancer in humans, and are classified by the
International Agency for Research on Cancer The International Agency for Research on Cancer (IARC; french: Centre International de Recherche sur le Cancer, CIRC) is an intergovernmental agency forming part of the World Health Organization of the United Nations. Its role is to conduct and ...
as a
group 1 Group 1 may refer to: * Alkali metal, a chemical element classification for Alkali metal * Group 1 (racing), a historic (until 1981) classification for Touring car racing, applied to standard touring cars. Comparable to modern FIA Group N * Group On ...
biological
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...
in 2009. ''O. viverrini'' is found in
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
, the
Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist ...
,
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
, and
Cambodia Cambodia (; also Kampuchea ; km, កម្ពុជា, UNGEGN: ), officially the Kingdom of Cambodia, is a country located in the southern portion of the Indochinese Peninsula in Southeast Asia, spanning an area of , bordered by Thailand t ...
. It is most widely distributed in northern Thailand, with high prevalence in humans, while central Thailand has a low rate of prevalence.


Discovery

''O. viverrini'' was first described by a French parasitologist Jules Poirier in 1886, who discovered the parasite in an Indian fishing cat (''Prionailurus viverrus''), originally from Southeast Asia, that died in the Zoological Gardens attached to the
National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with 7 ...
in Paris. He named it ''Distomum viverrini''. American parasitologists
Charles Wardell Stiles Charles Wardell Stiles (May 15, 1867 – January 24, 1941) was an American parasitologist born in Spring Valley, New York. He was notable for working on a campaign against hookworm infestation in the American South, where it had been found to cau ...
and Albert Hassall redescribed it and assigned it to the existing genus ''Opisthorchis'' (created by a French zoologist Raphaël Blanchard) in 1891. The first human specimen was described by a British parasitologist
Robert Thomson Leiper Robert Thomson Leiper (17 April 1881 – 21 May 1969) FRS CMG was a British parasitologist and helminthologist. Early life and education Leiper was born on 17 April 1881 in Witch Road, Kilmarnock, Scotland; the eldest of three children of John ...
in 1915, but without knowing the exact parasite. (He simply reported it as "Notes of the occurrence of parasites presumably rare in man.") Leiper received the specimens from an Irish medical doctor,
Arthur Francis George Kerr Arthur Francis George Kerr (1877–1942) was an Irish medical doctor. He is known particularly now for his botanical work, which was important for the study of the flora of Thailand. He encouraged other botanists to collect plant specimens in Tha ...
, who had collected them from the ''post mortem'' examination of two prisoners at a jail in
Chiang Mai Chiang Mai (, from th, เชียงใหม่ , nod, , เจียงใหม่ ), sometimes written as Chiengmai or Chiangmai, is the largest city in northern Thailand, the capital of Chiang Mai province and the second largest city in ...
, northern Thailand. In the next year, Kerr himself reported from investigation of 230 male prisoners that 39 (17 percent) of them had the infection. Kerr initially misidentified the parasite as ''O. felineus'', an already known human parasite, because of their close resemblance. C. Prommas also reported ''O. felineus'' in 1927 from an autopsy of a 17-year-old Thai male residing in
Roi Et Roi Et (, ) is a town (''thesaban mueang'') in north-eastern Thailand, capital of Roi Et Province. It covers the whole ''tambon'' Nai Mueang of Mueang Roi Et district. As of 2006 it had a population of 34,229. Roi Et is 514 km from Ban ...
, northeast Thailand. It was in 1955 when Elvio H. Sadun from the U. S. Public Health Service analysed the cases of opisthorchiasis in Thailand and concluded that all the infections were due to ''O. viverrini''. A systematic comparison in 1965 confirmed the differences from ''O. felineus''.


Description

Structurally, ''O. viverrini'' is basically similar to ''C. sinensis'' and ''O. felineus'', but it is slightly smaller than the two flukes. The body of an adult ''O. viverrini'' is flat (dorsoventrally flattened) like a leaf, shaped like a lancet, and can be seen through (transparent). They are
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...
, so no male or female individuals exist; each fluke has the complete sets of both male and female reproductive systems. A typical individual is 7 mm long and 1.5 mm wide. The anterior end is more pointed and marked by a mouth-like structure called oral sucker. About 1.5 mm behind the oral sucker is a similar structure called ventral sucker. These suckers are the organs of attachment. Two testes are seen towards the posterior end. The testes are lobed in contrast to the branched (dendritic) testes of ''C.sinensis''. It is connected to the
seminal vesicle The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder of some male mammals. They secrete fluid that partly composes the semen. The vesicles are 5 ...
, which is a coiled tube running up to the ejaculatory duct, which in turn opens through a small opening called genital pore just in front of the ventral sucker. Two ovaries are situated in front of the testes, and they form several lobes. The uterus runs along the ejaculatory duct and opens at the genital pore. A sac-like S-shaped tube called excretory bladder is between the two testes. The remaining body spaces are mostly occupied by a highly branched glandular organ called vitellaria (often called vitelline glands). Unlike the anterior end, the posterior end is rounded. The eggs of ''O. viverrini'' are 30 × 12 μm in size and they are slightly narrower and more regularly ovoid than in ''C. sinensis''. The eggs are visually indistinguishable in
Kato technique The Kato technique (also called the Kato–Katz technique) is a laboratory method for preparing human stool samples prior to searching for parasite eggs. Indications The Kato technique is now most commonly used for detecting schistosome eggs. I ...
smears from other eggs of flukes from other fluke family
Heterophyidae Heterophyidae is a family of intestinal trematodes in the order Plagiorchiida. Description: " Tegument covered by spines. Oral sucker not armed or armed by cyrcumoral spines. Pharynx presented. Genital synus presented. Ventral and genital suc ...
. The infective larvae,
metacercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...
, of ''O. viverrini'' are brownish and elliptical, with two nearly equal-sized suckers – the oral sucker and the ventral sucker. They are 0.19–0.25 × 0.15–0.22 mm in size.


Lifecycle

''O. viverrini'' is a
hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separ ...
liver fluke. Similar to ''C. sinensis'' and ''O. felineus'', it requires three different hosts to complete its lifecycle.
Freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs ...
s are the first intermediate hosts in which asexual reproduction takes place, and freshwater fishes belonging to the family
Cyprinidae Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...
) are second intermediate hosts in which larval development occurs. Fish–eating (piscivorous) mammals, including humans, dogs, and cats, act as definitive hosts, in which sexual reproduction occurs. As a result of poor
sanitation Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems ...
practices and inadequate
sewerage Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drainage, drains, manholes, pumping stations, storm overflows, a ...
infrastructure, ''O. viverrini''-infected people pass the trematode's eggs in their feces into bodies of fresh water from where snails become infected.


First intermediate host

The first intermediate hosts include freshwater snails of the genus ''Bithynia''. The only known host is '' Bithynia siamensis'' (that include all its three subspecies).
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(1995). ''Control of Foodborne Trematode Infection''. WHO Technical Report Series. 849
PDF part 1PDF part 2
page 89-91.
Snails are infected by the free-swimming larvae called
miracidia Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...
in water bodies where faecal matters of infected mammals are deposited. Inside the snail tissue, the miracidia grow into sposocysts, that contain spore-like daughter cells. The daughter cells called rediae multiply and develop into numerous larvae called
cercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...
. Each cercaria has a large head and a long tail. The cercariae escape from the snail and enter the water body again as free-swimming larvae. Their tails act as a propeller for swimming and they actively search for a fish host.


Second intermediate host

The cercaria then locates a cyprinoid fish, encysts in the fins, skin, and musculature of the fish, and becomes a
metacercaria Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...
. Habitats of second intermediate hosts of ''O. viverrini'' include freshwater habitats with stagnant or slow-moving waters (ponds, river, aquaculture, swamps, rice fields). In 1965, 9 fish hosts of ''O. viverrini'' were known.
JSTOR
Up to 2002, 15 species of fishes from seven genera of the family
Cyprinidae Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest verte ...
were known to serve as second intermediate host. Further research by Rim ''et al.'' (2008) showed an additional five host species. The known hosts include ''
Puntius brevis ''Puntius brevis'', sometimes known as the swamp barb (although ''Puntius chola'' is also known by that name), is a species of ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. Th ...
'', '' P. gonionotus'', '' P. orphoides'', '' P. proctozysron'', '' P. viehoeveri'', ''
Hampala dispar ''Hampala dispar'', also known as the Eye-spot barb or the Spotted hampala barbis a southeast Asian species of cyprinid, endemic to the basin of the Mekong. It is found in Thailand, Laos and Cambodia. Anatomy and appearance Hampala dispar has ...
'', '' H. macrolepidota'', '' Cyclocheilichthys armatus'', '' C. repasson'', ''
Labiobarbus lineatus ''Labiobarbus lineatus'' is a species of cyprinid fish found in Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Pen ...
'', ''
Esomus metallicus ''Esomus metallicus'', sometimes known as striped flying barb (although the common name is usually reserved for '' Esomus lineatus''), is a species of cyprinid found in Southeast Asia (Myanmar, Laos, Thailand, Cambodia, Vietnam, and Peninsular M ...
'', '' Mystacoleucus marginatus'', ''
Puntioplites falcifer ''Puntioplites falcifer'' is a species of ray-finned fish in the genus ''Puntioplites'' which is endemic to the Mekong basin in Thailand, Laos, Cambodia and Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Repub ...
'', ''
Onychostoma elongatum ''Onychostoma elongatum'' is a species of cyprinid in the genus ''Onychostoma''. It inhabits Laos and Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast A ...
'', '' Osteochilus hasseltii'', ''
Hypsibarbus lagleri ''Hypsibarbus lagleri'' is a species of ray-finned fish in the genus ''Hypsibarbus'' which is endemic to the middle Mekong basin in Cambodia, Laos and Thailand. It is fished for as a food fish and marketed fresh. ''Hypsibarbus lagleri'' has 8 so ...
'', and ''
Barbodes gonionotus The Java barb (''Barbonymus gonionotus''; th, ตะเพียน ''Ta-phian''; Lao language, Lao: ''Pa keng''; km, ត្រីឆ្ពិន ''Trey Chpin''; id, Tawes; Vietnamese language, Vietnamese: ''Mè Vinh'' ), more commonly known ...
''.


Definitive host

The metacercarial stage is infective to humans and other fish-eating mammals, including dogs, cats, rats, and pigs. Fish contain more metacercaria from September to February, before the dry season, and this is when humans are usually infected.
Infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
is acquired when people ingest raw or undercooked fish. Dishes of raw fish are common in the
cuisine of Laos Lao cuisine or Laotian cuisine ( lo, ອາຫານລາວ) is the national cuisine of Laos. The staple food of the Lao is sticky rice ( lo, ເຂົ້າໜຽວ, khao niao). Laos has the highest sticky rice consumption per-capita i ...
and the cuisine of Thailand: ''
koi pla ''Koi'' ( lo, ກ້ອຍ; th, ก้อย, ) is a "salad" dish of the Lao people living in modern-day Laos and Isan, Thailand, consisting of raw meat denatured by acidity, usually from lime juice. Common varieties include ''koi kung'' ( th, ...
'', raw fish in spicy salad ''
larb ''Larb'' ( lo, ລາບ; th, ลาบ, , , also spelled ', ', ' or ') is a type of Lao meat salad that is the national dish of Laos, along with green papaya salad and sticky rice Glutinous rice (''Oryza sativa var. glutinosa''; also ...
pla'', salted semi
fermented Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
fish dishes called ''
pla ra ''Pla ra'' ( th, ปลาร้า, ), similar to padaek in Laos, is a traditional Thai seasoning produced by fermenting fish with rice bran or roasted rice flour and salt fermented in a closed container for at least six months. Fermented fi ...
'', ''pla som'' and ''som fak''. The natural definitive host is the
leopard cat The leopard cat (''Prionailurus bengalensis'') is a small wild cat native to continental South, Southeast, and East Asia. Since 2002 it has been listed as Least Concern on the IUCN Red List as it is widely distributed although threatened by hab ...
(''Prionailurus bengalensis''). The young adult worm escapes from the metacercarial cyst in the upper small intestine and then migrates through the ampulla of Vater into the biliary tree, where it develops to sexual maturity over 4–6 weeks, thus completing the lifecycle. The adult worms primarily live in the bile duct, gall bladder, and sometimes in the pancreatic duct. Although they are hermaphrodites, reproduction is by cross fertilization (two individuals exchanging their gametes). Fertilized eggs are laid in the bile duct and are discharged along the bile juice into the intestine, and finally released in the environment along with the faeces. An individual fluke may shed as many as 200 eggs in a day. The exact lifespan is not known, but is estimated to be more than 25 years.


Prevalence

''O. viverrini'' remains a major public health problem in the Mekong Basin in Southeast Asia. It is endemic in Thailand, the Lao People's Democratic Republic, Vietnam, and Cambodia.It is most prevalent in Thailand, and for this reason Thailand has the highest incidence of opisthorchiasis-associated cancer,
cholangiocarcinoma Cholangiocarcinoma, also known as bile duct cancer, is a type of cancer that forms in the bile ducts. Symptoms of cholangiocarcinoma may include abdominal pain, yellowish skin, weight loss, generalized itching, and fever. Light colored stool ...
(CCA) in the world. About 9.6% of the total population of Thailand is estimated to be infected. It is most abundant in northern Thailand, while it occurs moderately in central Thailand. According to the five-year national survey from 2010 to 2015, the highest incidence reached up to 45.7% of the population in northern Thailand. However, there is no record of opisthorchiasis due to ''O. viverrini'' in southern Thailand. School children are most infected, and the infection was very high before 1984, after which there was mass treatment programme, and the prevalence sharply declined after 1994. A national survey in Lao PDR (under the project of Korea-Laos Collaborative Project for Control of Foodborne Trematode Infections in Lao PDR) between 2007 and 2011 indicates that it is the most prevalent helminth infection, amounting to 55.6% of the infection. It is not highly prevalent in Vietnam, but accurate survey is difficult because it is often co-infected with other flukes such as ''Haplorchis pumilio'', '' H. taichui'', and ''C. sinensis''. It is most abundant in the northern provinces. It is least prevalent in Cambodia. A national survey between 2006 and 2011 showed that it is the second most prevalent helminth accounting for 5.7% of the total infection, after
hookworm Hookworms are intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases. Hookworm infection is found in many parts of the world, and is common in areas with poor access to adequate water, sanitation, an ...
with 9.6% of the infection.


Effect on human health

Generally, opisthorchiasis due to ''O. viverrini'' is harmless without any clinical symptoms. Mild symptoms may appear such as
dyspepsia Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, or upper abdominal pain. People may also experience feeling full earlier t ...
, abdominal pain, constipation, or diarrhoea. However, under severe infection, enlargement of liver (
hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdomi ...
) and malnutrition are observed. In rare cases, cholangitis,
cholecystitis Cholecystitis is inflammation of the gallbladder. Symptoms include right upper abdominal pain, pain in the right shoulder, nausea, vomiting, and occasionally fever. Often gallbladder attacks (biliary colic) precede acute cholecystitis. The pain l ...
, and cholangiocarcinoma can also develop. In humans,''O. viverrini'' inhabits mainly the bile ducts, and rarely, the gall bladder and pancreatic duct. Heavy infection can produce problems in the liver, gall bladder, and bile ducts. The bile ducts of heavily infected patients are usually dilated and indicate
fibrosis Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perma ...
. Pathological effects on the bile ducts include inflammation, epithelial desquamation, goblet-cell metaplasia, epithelial and adenomatous
hyperplasia Hyperplasia (from ancient Greek ὑπέρ ''huper'' 'over' + πλάσις ''plasis'' 'formation'), or hypergenesis, is an enlargement of an organ or tissue caused by an increase in the amount of organic tissue that results from cell proliferati ...
, and periductal fibrosis. The collective effects in addition to specific parasite secretion and the host's immune reactions account for the development of cholangiocarcinoma. The infection is not immediately life-threatening; cancer develops after 30–40 years, but death occurs very fast, within 3–6 months of diagnosis.
Medical care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health profess ...
and loss of
wage A wage is payment made by an employer to an employee for work done in a specific period of time. Some examples of wage payments include compensatory payments such as ''minimum wage'', ''prevailing wage'', and ''yearly bonuses,'' and remuner ...
s caused by ''O. viverrini'' in Laos and in Thailand costs about million annually, primarily in northeast Thailand. Infections with ''O. viverrini'' and of other liver flukes in Asia affect the poor and poorest people. Opisthorchiasis has received less attention in comparison to other diseases, and it is a neglected disease in Asia.. There is no approved drug for the infection; however, Swiss researchers have tested
tribendimidine Tribendimidine is a broad-spectrum anthelmintic agent developed in China, at the National Institute of Parasitic Diseases in Shanghai. It is a derivative of amidantel.
and achieved a 70% cure rate. Surgery and supportive treatment are complicated and generally unavailable in the endemic areas. A general trematocide
praziquantel Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of helminthiasis, parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is us ...
is used for the infection, but is not technically recommended. In addition to praziquantel other commonly used anthelmintics such as
albendazole Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
,
artesunate Artesunate (AS) is a medication used to treat malaria. The intravenous form is preferred to quinine for severe malaria. Often it is used as part of Artemisinin-based combination therapy, combination therapy, such as artesunate plus mefloquine. I ...
, and
miltefosine Miltefosine, sold under the trade name Impavido among others, is a medication mainly used to treat leishmaniasis and free-living amoeba infections such as ''Naegleria fowleri'' and '' Balamuthia mandrillaris''. This includes the three forms of l ...
are found to be effective on the cercariae but not on the metacercariae. Its ability to cause cancer is worsened by the discovery that its infection is often associated with those of ''
Helicobacter ''Helicobacter'' is a genus of Gram-negative bacteria possessing a characteristic helical shape. They were initially considered to be members of the genus ''Campylobacter'', but in 1989, Goodwin ''et al.'' published sufficient reasons to justif ...
'' species (including ''
H. pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...
'', which is primarily associated with ulcers, but also may cause stomach cancers).


Genetics

''O. viverrini'' has 12 (six pairs) of
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s, i.e. 2n = 12. The draft genome and transcriptomes were published in 2014. Its genome is 634.5 MB in size. The species has 16,379 protein-coding genes.


See also

* The Integrated Opisthorchiasis Control Program


References

This article incorporates CC-BY-2.5 text from references.. and CC-BY-2.0 text from the reference..


Further reading

* * * * .


External links


Public Health Agency of Canada Opisthorchis spp. – Pathogen Safety Data Sheet

Genome info at WormBase

Info at Encyclopedia of Life

Taxonomy at UniProt


* ttp://www.stanford.edu/group/parasites/ParaSites2003/Opisthorchiasis/home.htm The Program in Human Biology, Stanford University {{Taxonbar, from=Q135523 Plagiorchiida IARC Group 1 carcinogens Infectious causes of cancer Foodborne illnesses Animals described in 1896 Parasitic helminths of humans Helminthiases Biliary tract disorders